Smart rectenna design for passive wireless power harvesting

ABSTRACT

The present technology is directed to a system and method for implementing passive power harvesting from ambient electromagnetic emissions with a smart rectenna that incorporates automatic frequency response tuning features. The disclosed system incorporates a tunable High Pass Filter and voltage multiplier rectifier with a front-end ultra wide band antenna unit. The frequency response of tunable components can be actively adjusted to match the frequency band containing most of the energy in the incident electromagnetic emission. A look up table is used for determining the appropriate biasing levels of the tunable components for each frequency in a frequency band of interest. By tuning a frequency response of impedance matching, filtering and rectifying components to correspond to a frequency region of maximum power spectral density in the incident energy signal, the system facilitates the scavenging of ambient electromagnetic energy from the spectral region with the highest power spectral density.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. Non-Provisional patentapplication Ser. No. 16/107,962, filed on Aug. 21, 2018, the fulldisclosure of which is hereby expressly incorporated by reference in itsentirety.

TECHNICAL FIELD

The present technology pertains to rectenna based ambient powerharvesting. More specifically it is directed to a tunable rectenna forambient power harvesting.

BACKGROUND

With the explosive and rapid development of wireless technologies, theambient wireless power density is growing due to an increasing number ofvarious electromagnetic power sources such as the cellular mobile basestations, digital TV towers and Wi-Fi routers. The idea of utilizing theradio frequency (RF) energy to power low-power electronic devices hasgained a lot of popularity in recent years as a replacement or asupplement to battery units in order to save maintenance cost. The useof batteries as an energy source has two disadvantages: the lifetime ofthe batteries is very limited even for low-power batteries, requiringimpractical periodical battery replacement, the use of commercialbatteries usually overkills the power requirements for low power (in therange of microwatts) sensor nodes, adding size and weight while creatingthe problem of environmental pollution due to the deposition of thesebatteries, as well as increases significantly the cost overhead ofdisposable nodes.

The meaning of Energy Harvesting (also called energy scavenging or powerharvesting), is the process by which energy from different sources iscaptured and stored. Generally, this definition applies to autonomousdevices that require a low amount of energy to function. Currently,energy harvesters do not provide sufficient amount of power to producemechanical movements or temperature changes (ovens, refrigerators, etc)because there aren't technologies that capture energy with greatefficiency.

Another advantage of energy harvesting technologies is that, unlike theproduction of large-scale power, the relevant energy sources arepractically free when taking into account, for example, theelectromagnetic energy of transmitting mobile stations and radio and TVbroadcasting antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the disclosure can be obtained, a moreparticular description of the principles briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only exemplary embodiments of the disclosure and are nottherefore to be considered to be limiting of its scope, the principlesherein are described and explained with additional specificity anddetail through the use of the accompanying drawings in which:

FIG. 1 illustrates a rectenna in accordance with some aspects of thepresent technology.

FIG. 2 illustrates a Power Spectral Density plot of a typical 2.4 GHzISM band with a 3 dB bandwidth of a standard passive rectenna inaccordance with some aspects of the present technology.

FIG. 3 illustrates an exemplary Lookup Table based approach for smartrectenna design, with an analog tuning feature, in accordance with someaspects of the present technology.

FIG. 4 illustrates two different example design implementation of atunable High Pass Filter in accordance with some aspects of the presenttechnology.

FIG. 5 illustrates an example smart rectenna design incorporating aLookup Table and digitally tunable components, in accordance with someaspects of the present technology.

FIG. 6 illustrates an example flow chart of operational steps forharvesting ambient energy using a tunable smart rectenna, in accordanceto some embodiments of the present technology

DESCRIPTION OF EXAMPLE EMBODIMENTS

Additional features and advantages of the disclosure will be set forthin the description which follows, and in part will be obvious from thedescription, or can be learned by practice of the herein disclosedprinciples. The features and advantages of the disclosure can berealized and obtained by means of the instruments and combinationsparticularly pointed out in the appended claims. These and otherfeatures of the disclosure will become more fully apparent from thefollowing description and appended claims, or can be learned by thepractice of the principles set forth herein.

Overview

Systems, methods, and devices are disclosed for implementing an optimalefficiency passive wireless power harvesting for a rectenna. Aspects ofthe technology are directed to deploying impedance matching, filteringand rectifying components having a tunable frequency response. Accordingto an embodiment, the frequency response of the one or more componentsmay be rendered tunable by utilizing one or more signal-controlledvariable elements (such as voltage controlled variable capacitors) inthe constructions of the components having a tunable frequency response.The frequency response of the rectenna's constituent components may thenbe tuned by one or more tuning signals generated in accordance to tuningparameters stored in a lookup table. The lookup table stored tuningparameters may comprise electrical parameters (i.e., voltage valuesrequired for adjusting/tuning a capacitance or inductance value of oneor more voltage-controlled capacitors or inductors in such a way so asto facilitate one or more desired output frequency responses)corresponding to various desired output frequency responses for eachinput radio frequency within a desired frequency band. The Lookup tablemay be stored/maintained on one or more non-volatile storage elementsand utilized to configure the one or more tuning signals depending onthe input radio frequency incident upon the front-end antenna unit. Thetuning signals may be analog or digital in nature.

Embodiment of the technology provide a system for passive wireless powerharvesting, comprising of first component, having a first tunablefrequency response, and a first input side configured to receive a radiofrequency electrical signal from an antenna, as well as a second inputside configured to receive one or more tuning signals. The firstcomponent additionally includes an output side electrically coupled toan input side of a second component which also has a tunable frequencyresponse. The second component, in addition to having an input side forelectrically coupling to the output of the first component, may alsoinclude another input side that is configured to receive one or moretuning signals. The output of the second component may then beconfigured to deliver a DC electrical signal to a load.

The system as provided by embodiments of the disclosed technology mayalso include a computer-readable storage element for storing a lookuptable. The lookup table may be utilized for storing relevant informationfor configuring the one or more tuning signals. For example theinformation in the lookup table may include one or more parameters foroptimally tuning the tunable frequency responses of the first and thesecond components for one or more selected spectral bands.

Embodiments of the disclosed technology also describe a method forimplementing passive wireless power harvesting. The example method foreffectively accomplishing passive wireless power harvesting may includelooking up one or more stored tuning parameters corresponding to one ormore desired spectral bands, to thereby produce a desired frequencyresponse in one or more tunable components of a rectenna. The desiredfrequency response may correspond to an optimal power transfer, in oneor more desired spectral bands, to and from the one or more tunablecomponents. By transmitting the one or more stored tuning parameters tothe one or more tunable components, as prescribed by embodiments of thedisclosed method, a frequency response of the one or more tunablecomponents may be accordingly adjusted in such a way so as to maximizepower transfer within the one or more desired spectral bands.

In some embodiments of the technology, the first component may comprisea high pass filter, and include a section for providing impedancematching between the antenna and the second component. Other possiblefeatures of the first component may include one or more voltagecontrolled capacitors utilized to facilitate the tunable frequencyresponse of the first component. With respect to the lookup table, theone or more parameters that are stored in the lookup table for use inoptimally configuring the one or more tuning signals, may comprises oneor more voltage values. These lookup table stored voltage values maythen be transmitted to the first component in order to tune the one ormore voltage controlled variable capacitors of the first component insuch a way to, for example, provide impedance matching between theantenna and the second component. This will increase an amount of powertransferred from the first component to the second component within theone or more selected spectral bands.

The second component, in some embodiments, may comprise a rectifierunit, to provide the necessary rectification of the antenna's AC signal.Moreover the second component may also include a voltage multiplicationunit. In some embodiment, a voltage doubling capability may suffice forproducing a desired outcome, therefore in some embodiments the secondcomponent may include a voltage doubling unit in addition to a rectifierunit. The second component may further comprise a section for providingimpedance matching to the load. The second component may also feature atunable frequency response. In some embodiments, a tunable frequencyresponse may be facilitated by one or more voltage controlled variablecapacitors in the second component. Therefore the one or more parametersbased on which the one or more tuning signals may be configured, maycomprise one or more voltage values for tuning the one or more voltagecontrolled variable capacitors of the second component. The tuningoperation then provides for maximum power transfer for each of aplurality of input radio frequencies in the one or more selectedspectral bands.

EXAMPLE EMBODIMENTS

Disclosed are systems, methods, for smart Rectenna design with frequencyresponse tuning features to dynamically adjust a frequency response ofthe Rectenna system to appropriate range that optimizes the operation ofthe system and maximizes the harvested power. Various embodiments of thedisclosure are discussed in detail below. While specific implementationsare discussed, it should be understood that this is done forillustration purposes only. A person skilled in the relevant art willrecognize that other components and configurations may be used withoutparting from the spirit and scope of the disclosure.

Wireless energy harvesting by using rectifying antenna (rectenna)technologies is a feasible solution to convert the ambientelectromagnetic power to a usable DC power. A rectenna, rectifyingantenna, is a special type of antenna that is used to convertelectromagnetic energy into direct current (DC) electricity. Rectennasare widely adopted devices for the wireless power transmission andenergy harvesting. A rectenna is a passive element with rectifyingdiodes that operates without an internal power source. It can receiveand rectify electromagnetic power to DC electrical power. A simplerectenna element may consist of a dipole antenna with a radio frequency(RF) diode connected across the dipole elements. The diode rectifies theAlternating Current (AC) induced in the antenna by the electromagneticradiation to produce Direct Current (DC) power which powers a loadconnected across a diode. Schottky diodes are usually used because theyhave a low voltage drop and high speed and therefore have low powerlosses due to conduction and switching.

A general block diagram of an example rectenna 100 is shown in FIG. 1.Rectenna 100 consists of a receiving antenna 102 which captureselectromagnetic (EM) waves 104, and an EM-to-DC (electromagnetic energyto direct electrical current) rectifying circuit 106 which converts thereceived electromagnetic energy 104 into electrical energy. The EM-to-DCconversion process produces high order harmonic components because ofthe non-linear characteristic of diodes (or transistors) components.These frequency components are highly unwanted; they could decreaseefficiency and create electromagnetic pollution; and it is essential tofilter them. An input high frequency (HF) filter 108, placed between theantenna 102 and the rectifier 106 provides impedance matching betweenthe antenna 102 and the diode rectifier 106 around a central frequency(˜2.45 GHz) for better power transfer. In effect HF filter 108introduces additional impedance between antenna 102 and the rectifier106 in such way the input impedance of rectifier 106 is better matchedwith output impedance of the previous stage that is electrically coupledto it. This will increase the power transfer from antenna 102 torectifier 106 as well as reduce signal reflection resulting frommismatch between the output impedance of the antenna 102 and inputimpedance of the rectifier 106.

Referring back to the example rectenna 100 in FIG. 1, the input HFfilter 108 further prevents high order harmonics to be radiated by theantenna into the rectification circuitry. This approach improves theamount of power transferred between the antenna and the rectifier andalso the electromagnetic to electrical (DC) energy conversionefficiency. After rectification, an output DC filter 110 transmits theDC component to a load 112 and filters out all high frequencies (HF).Thereby, all high order harmonics are confined between the input HFfilter 108 and the DC output filter 110.

As addressed earlier, the use of rectennas is an efficient way forharvesting ambient electromagnetic (EM) energy, which is a solution fortrickle charge and battery life extensions for indoor low power Internetof Things (IoT) devices for both home and enterprise devices. Howeverrectennas have to be optimized or tuned to a particular frequencyresponse in order to maximize energy harvesting at input frequencies ofinterest. As such, most rectenna implementations are tuned to a specificfrequency region and hence do not have the flexibility to captureambient electromagnetic energy from other frequency region. If thefrequency region for which a rectenna is optimized does not coincidewith the frequency region of maximum power spectral density (PSD) in theincident electromagnetic energy signal, the overall conversionefficiency of the rectenna will drop significantly. This idea may bebetter explained by referencing FIG. 2 which shown a trace diagram 200consisting of an indicia 202 representing a 3 dB bandwidth of a passiverectenna and a Power Spectral Density (PSD) plot 204 for a typical 2.4GHz ISM Band.

The industrial, scientific, and medical radio band (ISM band) refers toa group of radio bands or parts of the radio spectrum that areinternationally reserved for the use of radio frequency (RF) energyintended for scientific, medical and industrial requirements rather thancommunication. ISM equipment generates electromagnetic interference thatinterrupts radio communications that make use of the same frequency.Therefore, such equipment were restricted to specific frequency bands.However there has been a rapid growth in the use of ISM band inlow-power, short-range communications platforms. Bluetooth devices,cordless phones, Wi-Fi computer networks, and Near Field Communication(NFC) devices all make use of ISM bands. In 1985, the U.S. FederalCommunications Commission opened the ISM bands for use in mobilecommunications and wireless LANs.

Referring back to FIG. 2, the PSD plot 204 represents the energy/power(in terms of gain) contained in different frequency components of atypical ISM band RF signal. The bandwidth of a passive rectenna (rangeof frequencies outside of which the gain of the device falls by 50% or 3dB) is represented by a frequency range 202 centered around a primaryfrequency (˜2.45 GHz) 206. What this means is that for a passiverectenna design the frequency region corresponding to rectenna's maximumconversion efficiency is centered on a single frequency 206 with alimited 3 dB bandwidth 202 extending around the center frequency 206.

Therefore, as can be observed from FIG. 2, the frequency regioncorresponding to the maximum power spectral density in an incidentenergy signal may not fall within a frequency range 202 corresponding tothe bandwidth of a passive rectenna. Therefore a passive architecturemay or may not be harvesting ambient electromagnetic energy from theregion of maximum PSD. Alternatively, a frequency agile recetannaarchitecture capable of shifting its operational center frequency to theregion of maximum power spectral density in the incident electromagneticsignal would maximize electric power harvested from the incidentelectromagnetic signal.

Aspects of the present technology describe a solution for improvingelectromagnetic to electrical DC energy conversion efficiency in arectenna. Embodiments of the present technology include a system andmethod for implementing a smart rectenna capable of adjusting itsfrequency response to the spectral region of the maximum power spectraldensity in the incident energy signal, to thereby achieve improvedconversion efficiency.

Some embodiments of the present technology describe a system and methodbased on pairing an Ultra Wideband (UWB) front end antenna with aholistically frequency tunable rectifying circuit to thereby implement asystem directed at standardizing conversion efficiency over a widefrequency band.

A rectenna's total efficiency in converting ambient electromagneticenergy (i.e., incident Radio Frequency (RF) signal) to Direct Current(DC) electrical energy) depends upon the efficiency factors associatedwith the performance of its key components. One such factor involves theefficient absorption of the incident RF signal at the desired frequency.Another contributing factor to the total efficiency of the rectenna isthe performance efficiency of the impedance matching stage between theantenna unit and the rectifier to thereby ensure good power transfer tothe rectification circuitry of the rectenna. Improving rectenna totalconversion efficiency also necessitates an efficient impedance matchingstage between the rectifier and output load to minimize signal loss intransferring the rectified DC signal (output of the rectifier unit) tothe load. It is also important, with respect to improving totalefficiency of rectenna, to minimize the power loss through therectification diode (represented by the voltage drop across the diode).

In accordance with some embodiments of the present technology, theantenna efficiency criteria (involving RF absorption at desiredfrequencies) is addressed by utilizing an Ultra Wideband (UWB) antennawith bandwidth exceeding 7 GHz in the design with an smart rectenna, asdisclosed herein. The smart rectenna provides for near uniform antennaefficiency over the wide bandwidth supported by the Ultra Wideband (UWB)antenna.

The smart functionality of the proposed rectenna system, in accordancewith some embodiments, is implemented by actively modulating biasvoltage levels of one or more tunable components in such a way so as toa tune their operation to a desired frequency range associated withincident electromagnetic signal. In some embodiments, this is achievedthrough the use of a Lookup Table (LUT) in conjunction with Digital toAnalog Converter (DAC) to directly change the bias level on one or moreanalog tunable components constituting the smart rectenna.

FIG. 3 illustrates a system diagram for an exemplary smart rectenna 300implemented in accordance with some embodiments of the presenttechnology. Rectenna 300 comprises an Ultra Wideband (UWB) Antenna 302connected to voltage doubling rectifier unit 304 through a high passfilter 306. The output of the voltage doubling rectifier unit 304 is aDC electrical signal that is provided across the load 308 which maycomprise any power consuming or storing device.

The Voltage doubling rectifier unit 304 performs a rectification of theAntenna's sinusoidal AC voltage output in order to convert it to a DCvoltage. However, due to the very low voltages induces in the antenna,the voltage doubling rectifier unit also acts as a voltage doubler, bydoubling the voltage amplitude in order to reach higher DC voltagelevels for the same input power.

The exemplary smart rectenna 300 also features a digital domain 310which further comprises a controller unit 311. The controller unit 311generates the appropriate control signal required to tune the operationof high pass filter 306 and voltage doubling rectifier unit 304 to adesired frequency range. The digital domain 310 also comprises a Digitalto Analog Converter (DAC) 312 which couples an output of the controllerunit 311 to the High Pass Filter 306. DAC 312 converts the digitalcontrol signal 313, generated by controller unit 311, to an analogtuning signal 314 for adjusting the biasing state of the tunable HighPass Filter 306. The digital domain 310 also includes a second Digitalto Analog Converter (DAC) unit 316 which connects to the voltagedoubling rectifier 304 and converts the digital control signal 318,generated by the controller unit 311, to an analog tuning signal 320.The analog signal 320, in turn, controls a biasing state of the tunablevoltage doubling rectifier 304. The digital control domain of theexemplary rectenna system 300 also includes a memory element 322 forstoring a Lookup Table 324. The tuning action of the controller unit311, directed at the tunable components 306 and 304, is moderated by theinformation retrieved from the Lookup Table 324.

Comparing the example smart rectenna 300 from FIG. 3 to the conventionalrectenna 100 from FIG. 1, it is observed that the exemplary smartrectenna 300 achieves rectifier to load impedance matching with a simpletunable voltage multiplier rectifier circuit, represented as voltagedoubling rectifier unit 304 in FIG. 3, instead of a low pass filter,represented as DC filter 110 in FIG. 1. As described earlier, voltagedoubling rectifier circuit 304 has a tunable frequency response that maybe adjusted by the controller unit 311 using a Lookup Table 324.

Frequency response is a quantitative measure of the output frequencyspectrum of a system or device in response to a stimulus, and may beused to characterize the dynamics of the system. In other words, it is ameasure of magnitude and phase of the output signal as a function ofinput signal frequency. Frequency response of a system is often relatedto the RC time constant of the system. RC time constant, which is equalto the product of the circuit resistance and circuit capacitance,relates to the charge and discharge time of various capacitances throughtheir associated resistors.

The frequency response of the circuit is made adjustable by usingtunable capacitors 326 and 328 in the construction of the exemplaryvoltage-doubler rectifier 304.

The voltage doubler rectifier 304 may be considered as a modification ofthe single shunt diode configuration. The positive half cycle of thealternating input signal 325 (produced at the output of 306) inputtedinto 304 is rectified by the series diode 326 and the energy is storedin signal-controlled variable capacitor 328. The negative half cycle ofthe wave is rectified by the shunt diode 330 and the energy is stored insignal-controlled variable capacitor 332. The energy insignal-controlled variable capacitor 332 can be transferred to thesignal-controlled variable capacitor 328 so that the voltage across thesignal-controlled variable capacitor 328 is approximately two times ofthe peak voltage in the single series diode configuration. The breakdownvoltage of the rectifier is increased hence the theoretical maximumconversion efficiency of the rectifier is also improved. Moreover, thebiasing voltage of diode 326 is provided by using part of the rectifiedwave from diode 330 which reduces the input radio frequency powerrequirement (hence improving the power sensitivity). The tuningmechanism of signal-controlled variable capacitors 332 and 328 may bebased on voltage control, current control or by other means ofmodulating electrical characteristics of the tunable capacitors thatwould be known to a person of ordinary skill in the arts.

Similarly the tunable high pass filter component 306 may be constructedusing tunable capacitors (signal-controlled variable capacitors) asillustrated in FIG. 4 by exemplary filter circuits 402 and 404. Filtercircuit 402 and 404 represent a T-Type and a π-type high Pass Filters,respectively. High Pass Filters can tap into a radio frequencytransmission path and block the lower frequency bands allowing just thehigher frequencies to pass. High Pass Filter circuit 402 comprises twotunable capacitors C_(t1), C_(t2) connected in series and an inductor L₁connected between the common node 406 and the ground terminal 408. Thetunable capacitors C_(t1) and C_(t2) are serially connected in the pathconnecting the input and output terminals 410 and 412.

High Pass Filter circuit 404 comprises one tunable capacitor C_(t3)disposed in the path connecting the input and the output terminal 414and 416, respectively. Tunable capacitor C_(t3) is surrounded by twoinductors and L₂ and L₃ that provide a low-frequency path to the groundterminal 410 on either side of capacitor C_(t3). The inductors, L₂ andL₃, shunt out the lower frequencies. in accordance to an embodiment,tunable capacitors. C_(t1), C_(t2) and C_(t3) may comprise voltagecontrolled variable capacitors.

Referring back to FIG. 3, the utility of the Lookup Table 324 as part ofthe smart rectenna design 300, as disclosed by some embodiments, is thatit can be pre-programmed with a list output configuration (for examplebias levels) for a variety of specific input frequency conditions. Thisconfiguration obviates a need for performing any data processing on therectenna system or for example on the wireless Internet of Things (IoT)sensor/device connected thereto. In this way the entire wirelesscharging circuitry (i.e., rectenna system) becomes a digital/analogslave device. This eliminates the processing load on the wireless sensoror the rectenna unit, thereby drastically reducing the power overhead ofrunning the rectenna circuitry.

In some embodiments, every band and channel center frequency for the 2.4GHz-5 GHz ISM bands may be pre-programmed into the Look up Table.

As described in reference to FIG. 3, controller unit 311 generatesdigital control signal 313 and 318 based on information retrieved fromLookup Table 324. The DAC units 312 and 316 convert the digital controlsignals 313 and 318 to analog signals 314 and 320 that are fed throughto one or more signal-controlled variable capacitive elements of theanalog-tunable components 306 and 304. In some embodiments, the analogtuning signals 314 and 320 interface with one or more signal-controlledvariable capacitive elements of the analog-tunable components 306 and304, in order to modify their electrical properties in such a way so asto cause the frequency response of the one or more analog-tunablecomponents to match the dynamic conditions of the ambient input energysignal. In some embodiments of the present technology one or ore digitalcontrol signals, generated based on information retrieved from theLookup Table, directly interface with digitally tunable circuitcomponent of a smart rectenna as shown in FIG. 5.

FIG. 5 illustrates an exemplary digitally tunable rectenna 500. Withreference to system 500, signal processing and conditioning operationstake place entirely within the digital domain 502. The configuration ofsystem 500 only differs from that of system 300 in that it utilizes adigital tunable High Pass Filter 504 and a digital tunable voltagedoubling rectifier 506, thereby obviating a need for DAC units 312 and316. Similar to operation of the smart rectenna 300, the controller unit508 generates digital tuning signals 510 and 512 based on informationretrieved from the Lookup Table. However unlike the smart rectenna 300,the control signals 510 and 512 can directly interface with thedigitally tunable circuit components 504 and 506, respectively.Therefore no Digital to Analog Converter (DAC) units are required incase of the exemplary smart rectenna 500. The tradeoff between theanalog and digital approach is that the analog approach results in afaster tuning speed and a slightly lower power consumption, however itis more expensive in terms of additional circuit components than apurely digital approach.

In some embodiments of the present technology, the region of maximumpower spectral density region in the incident electromagnetic energysignal may be discovered by using the approximate distances between thetarget device (device with the power harvesting rectenna circuitryembedded inside) and one or more nearest sources of electromagneticradiation. In this way it would be possible to estimate path lossbetween the target device and the sources of electromagnetic energysignal (Free Space Path Loss model is an example of one such method). Inaccordance to an embodiment, a weighted algorithm that takes both thepath loss and the wireless spectrum congestion (a metric that can bedetermined by methods similar but not limited to Clear ChannelAssessment) may then be used to obtain the frequency region of maximumpower spectral density in the incident electromagnetic energy signal.

Since all of these calculations and determinations will be done on thewireless network management infrastructure and not on the target devicethere is no power cost to the target device.

In accordance to some embodiments of the present technology, once thedetermination is made to change the channel (frequency response of thetunable components of the smart rectenna system), a simple low powercommunication protocol such as but not limited to Bluetooth will be usedto send this data to the target device.

Flow chart 600 illustrated in FIG. 6 provides an operational overviewfor ambient energy harvesting using a tunable smart rectenna inaccordance to some embodiments of the present technology. According tothe example flowchart 600, spectral bands corresponding to greatestpower spectral density (PSD) in the incident electromagnetic signal aredetermined at step 602. The operation then moves to step 604 wherein aLookup Table containing circuit tuning parameters for frequencies inselect spectral bands are searched or looked up. In some embodiments,circuit tuning parameters corresponds to parameters for tuning thefrequency response of the circuit/element or component.

Referring back to flow chart 600, at step 604, circuit tuning parameterscorresponding to the desired frequencies regions (incident frequencieswith greatest PSD determined in step 602) are identified in the LookupTable. At step 606, the information, corresponding to the identifiedparameters is communicated or transmitted to the relevant components(i.e., tunable components of the smart rectennas) or the relevantvariable electrical elements (i.e., voltage controlled variablecapacitors in the tunable components of the smart rectenna). Thecommunication may be accomplished via analog or digital signals. Uponreceiving the aforementioned parameters, at step 608, the frequencyresponse of the tunable components (or the value of variable electricalelement) is adjusted accordingly to maximize power transfer betweendifferent components of the smart rectenna and improve the efficiency ofconverting incident electromagnetic energy to direct-current electricalenergy.

For clarity of explanation, in some instances the present technology maybe presented as including individual functional blocks includingfunctional blocks comprising devices, device components, steps orroutines in a method embodied in software, or combinations of hardwareand software.

In some embodiments the computer-readable storage devices, mediums, andmemories can include a cable or wireless signal containing a bit streamand the like. However, when mentioned, non-transitory computer-readablestorage media expressly exclude media such as energy, carrier signals,electromagnetic waves, and signals per se.

Methods according to the above-described examples can be implementedusing computer-executable instructions that are stored or otherwiseavailable from computer readable media. Such instructions can comprise,for example, instructions and data which cause or otherwise configure ageneral purpose computer, special purpose computer, or special purposeprocessing device to perform a certain function or group of functions.Portions of computer resources used can be accessible over a network.The computer executable instructions may be, for example, binaries,intermediate format instructions such as assembly language, firmware, orsource code. Examples of computer-readable media that may be used tostore instructions, information used, and/or information created duringmethods according to described examples include magnetic or opticaldisks, flash memory, USB devices provided with non-volatile memory,networked storage devices, and so on.

Devices implementing methods according to these disclosures can comprisehardware, firmware and/or software, and can take any of a variety ofform factors. Typical examples of such form factors include laptops,smart phones, small form factor personal computers, personal digitalassistants, and so on. Functionality described herein also can beembodied in peripherals or add-in cards. Such functionality can also beimplemented on a circuit board among different chips or differentprocesses executing in a single device, by way of further example.

The instructions, media for conveying such instructions, computingresources for executing them, and other structures for supporting suchcomputing resources are means for providing the functions described inthese disclosures.

Although a variety of examples and other information was used to explainaspects within the scope of the appended claims, no limitation of theclaims should be implied based on particular features or arrangements insuch examples, as one of ordinary skill would be able to use theseexamples to derive a wide variety of implementations. Further andalthough some subject matter may have been described in languagespecific to examples of structural features and/or method steps, it isto be understood that the subject matter defined in the appended claimsis not necessarily limited to these described features or acts. Forexample, such functionality can be distributed differently or performedin components other than those identified herein. Rather, the describedfeatures and steps are disclosed as examples of components of systemsand methods within the scope of the appended claims.

What is claimed is:
 1. A system comprising: a first component having afirst tunable frequency response, the first component comprising a firstinput side configured to receive a radio frequency electrical signalfrom an antenna, a second input side configured to receive one or moretuning signals, and a first output side; a second component having asecond tunable frequency response, the second component comprising athird input side electrically coupled to the first output side of thefirst component, a fourth input side configured to receive one or moretuning signals and a second output side configured to deliver a directcurrent (DC) electrical signal to a load; and a computer-readablestorage medium having stored thereon a lookup table, wherein the one ormore tuning signals are configured based on information in the lookuptable, wherein the information in the lookup table comprises one or moreparameters to tune the first tunable frequency response of the firstcomponent and the second tunable frequency response of the secondcomponent for one or more selected spectral bands.
 2. The system ofclaim 1, wherein the first component comprises a high pass filter. 3.The system of claim 1, wherein the first component further comprises asection that provides impedance matching between the antenna and thesecond component.
 4. The system of claim 1, wherein the first componentfurther comprises one or more voltage controlled variable capacitorsthat facilitate the first tunable frequency response.
 5. The system ofclaim 4, wherein the one or more parameters comprise one or more voltagevalues to tune the one or more voltage controlled variable capacitors ofthe first component to thereby increase an amount of power transferredfrom the first component to the second component within the one or moreselected spectral bands.
 6. The system of claim 5, wherein the one ormore tuning signals for tuning the first tunable frequency response ofthe first component comprise at least one of analog signals or digitalsignals.
 7. The system of claim 1, wherein the second componentcomprises a rectifier unit.
 8. The system of claim 1, wherein thecomputer-readable storage medium comprises one or more non-volatilestorage elements.
 9. The system of claim 1, wherein the second componentfurther comprises a voltage doubling unit.
 10. The system of claim 1,wherein the second component further comprises a section for providingimpedance matching to the load.
 11. The system of claim 1, wherein thesecond component further comprises one or more voltage controlledvariable capacitors to facilitate the tunable frequency responses. 12.The system of claim 11, wherein the one or more parameters furthercomprise one or more voltage values to tune the one or more voltagecontrolled variable capacitors of the second component for maximum powertransfer for each of a plurality of input radio frequencies in the oneor more selected spectral bands.
 13. The system of claim 1, wherein theone or more tuning signals for tuning the second tunable frequencyresponse of the second component comprises at least one of analogsignals or digital signals.
 14. A method comprising: configuring one ormore tuning signals based on information from a lookup table, theinformation comprising on one or more parameters corresponding to one ormore desired spectral bands; and transmitting the one or more tuningsignals to a first component of a rectenna and a second component of therectenna, wherein the first component has a first tunable frequencyresponse and comprises a first input side configured to receive a radiofrequency electrical signal from an antenna, a second input sideconfigured to receive the one or more tuning signals, and a first outputside, and wherein the second component has a second tunable frequencyresponse and comprises a third input side electrically coupled to thefirst output side of the first component, a fourth input side configuredto receive the one or more tuning signals, and a second output sideconfigured to deliver a direct current (DC) electrical signal to a load.15. The method of claim 14, wherein the one or more tuning signals areconfigured to tune the first tunable frequency response of the firstcomponent for the one or more desired spectral bands based on the one ormore parameters.
 16. The method of claim 14, wherein the one or moretuning signals are configured to tune the second tunable frequencyresponse of the second component for the one or more desired spectralbands based on the one or more parameters.
 17. The method of claim 14,wherein the first component comprises a high pass filter.
 18. The methodof claim 14, wherein the one or more parameters comprise one or morevoltage values to tune one or more voltage controlled variablecapacitors of the first component to thereby increase an amount of powertransferred from the first component to the second component within theone or more desired spectral bands.
 19. The method of claim 14, whereinthe second component comprises a rectifier unit.
 20. The method of claim14, wherein the one or more parameters comprise one or more voltagevalues to tune one or more voltage controlled variable capacitors of thesecond component for maximum power transfer for each of a plurality ofinput radio frequencies in the one or more desired spectral bands.